It is well known that the urethane linkages of polyurethane foams are formed by the exothermic reaction of a polyfunctional isocyanate and a polyfunctional active hydrogen-containing compound in the presence of a catalyst, and that the cellular structure of the foam is provided by gas evolution and expansion during the urethane-forming reaction. In accordance with the "one-shot process" which is the most widely used industrial technique, direct reaction is effected between all of the raw materials which include the polyisocyanate, the active hydrogen-containing compound, the catalyst system, blowing agent, surfactant, and, optionally, a flame retardant. A major function of the surfactant is to stabilize the polyurethane foam, that is, prevent collapse of the foam until the foamed product has developed sufficient gel strength to become self-supporting.
It is also well known that suitable active hydrogen-containing compounds include polyether polyols and polyester polyols. From the standpoint of their chemical structure, therefore, polyurethane foams are usually classified as polyether and polyester polyurethane foams, respectively. Polyurethane foams also differ with respect to their physical structure and, from this standpoint, are generally classified as flexible, semi-flexible or rigid foams.
Although certain techniques of polyurethane foam manufacture such as the "one-shot process" and certain components of the polyurethane foam formulation such as the polyisocyanates, amine catalyst and blowing agent, are generally useful, a specific problem associated with the production of a particular type of polyurethane foam and the solution thereto are often peculiar to the particular chemical and physical structure of the desired foamed product. Thus, a significant development in the production of a polyether polyurethane foam or a rigid polyurethane foam, for example, may not be generally applicable to the production of other foamed products. In particular, the efficacy of the foam stabilizer is usually selective with respect to the formation of a particular type of foam. For example, although flexible polyester polyurethane foam was originally made using conventional organic surfactants or emulsifiers, such compounds were not effective for the manufacture of flexible polyether polyurethane foam. As polyurethane foam technology advanced and the end-uses became more varied, it became apparent that certain deficiencies in the quality of flexible polyester polyurethane foam such as the presence of splits and a nonuniform cell structure were attributable, at least in part, to the organic surfactants employed. However, the mere substitution of the organic surfactants with various polysiloxane-polyoxyalkylene block copolymers which had been used as foam stabilizers with satisfactory results in the production of other types of polyurethane foams (e.g., in the production of polyether polyurethane foams and certain rigid polyester polyurethane foams), did not produce completely satisfactory flexible polyester polyurethane foams.
The search for improved surfactants for stabilization of low density flexible polyester polyurethane foams is further complicated by the need for a foam stabilizing surfactant having wide processing latitude (i.e., a foam stabilizing surfactant which, when employed in various concentration amounts of wide latitude, produces polyurethane foams having desirable physical properties including high cell counts). For example, when low cell counts or other undesirable physical properties appear in low density flexible polyester polyurethane foam, an increased or decreased amount of foam stabilizing surfactant is applied to remedy the particular problem. However, increasing or decreasing the amount of foam stabilizing surfactant in low density flexible polyester polyurethane foam formulation will not necessarily result in high cell counts or other desirable physical properties. Therefore, a foam stabilizing surfactant having wide processing latitude is essential for overcoming variations encountered in low density flexible polyester polyurethane foam formulation.
A significant development in polyester polyurethane foam manufacture was the discovery that a satisfactory combination of uniform cell structure and freedom from splits was achieved by using a particular combination of foam stabilizing ingredients. This latter combination comprises (a) an anionic organic surfactant that is soluble in the polyester polyol reactant at room temperature and that is capable of lowering the surface tension of the polyester resin reactant when dissolved therein and (b) a polysiloxane-polyoxyalkylene block copolymer surfactant characterized by a particular molecular weight (from 500 to 17,000), siloxane content (from 14 to 40 weight percent based on the weight of the copolymer) and oxyethylene content (at least 75 weight percent based on the total amount of oxyalkylene groups in the copolymer). This particular advance in polyester polyurethane foam manufacture is described in greater detail in U.S. Pat. No. 3,594,334. A foam stabilizer of the class described in the latter patent is that referred to herein as comparative Organosiloxane Composition PP. It is found that comparative Organosiloxane Composition PP is capable of stabilizing low density polyester polyurethane foam having some desirable physical properties at a very narrow concentration range. However, comparative Organosiloxane Composition PP does not perform as well as desired in all cases in overcoming the many variations encountered in low density flexible polyester polyurethane foam formulation.
Several other patents broadly disclose the use of organosiloxane compositions ranging from low molecular weight to high molecular weight but exemplifying only high molecular weight compositions, as foam stabilizers in flexible polyester polyurethane foam formulation. U.S. Pat. No. 3,979,419 exemplifies high molecular weight (e.g., 2700 to 4600) organosilicone compositions modified by both cyanobearing ether groups and polyoxyalkylene units as demonstrated by Surfactants A through J in the working Examples. These organosilicone compositions are useful as foam stabilizers in the manufacture of flexible polyester polyurethane foam and offer particular advantage in the formation of flame-retarded foam. U.S. Pat. No. 3,954,824 exemplifies high molecular weight (e.g., 2500 to 5400) organosilicone polymers modified by both cyanoalkyl groups and polyoxyalkylene units as demonstrated by Surfactants A through F in the working Examples. These organosilicone polymers are also useful as foam stabilizers in the manufacture of flexible polyester polyurethane foam including flame-retarded foam. U.S. Pat. No. 3,793,360 relates to organosilicone polymers containing monomeric units A, B and C where A is an inorganic tetrafunctional unit (SiO.sub.4/2) in which each of the four valences of silicon is associated with oxygen, B is a polyfunctional siloxy unit in which silicon is bonded to at least one organic moiety bearing a polyoxyalkylene chain, and C is a monofunctional triorganosiloxy unit. These organosilicone polymers have beneficial utility as foam stabilizers in the manufacture of flexible polyester polyurethane foam. However, none of the latter mentioned patents exemplify low molecular weight organosiloxane compositions as described in this invention nor disclose their use as foam stabilizers in the manufacture of low density flexible polyester polyurethane foam.
Several other patents broadly disclose organosiloxane compositions having a wide molecular weight range including low molecular weight organosiloxane compositions as described in this invention. U.S. Pat. No. 3,905,924 discloses cyanoalkyl modified siloxane fluids and the use of these fluids as foam stabilizers in the production of high resilience polyether urethane foam. U.S. Pat. No. 2,872,435 describes (cyanoalkoxy)alkyl substituted organosilicon compounds having peculiar properties in their own rights as fluids, rubbers and resins. The (cyanoalkoxy)alkyl substituted organosilicon compounds are employed as intermediates for the preparation of amide or carboxylic substituted organosilicon compounds and further provide organosilicon rubbers and resins which have an improved resistance to attack by organic solvents and oils. U.S. Pat. No. 3,741,917 relates to ether modified siloxane block copolymers and the use of these copolymers as foam stabilizers in the production of cold cure polyether urethane foam having high resiliency. U.S. Pat. No. 3,879,433 discloses certain hydroxyalkylsiloxanes that are particularly useful as foam stabilizers in rigid polyether polyurethane foam formulation. U.S. Pat. No. 3,686,254 and U.S. Pat. No. 3,657,305 describe aralkyl modified siloxane fluids useful in the preparation of siloxane-polyoxyalkylene block copolymers. The siloxane-polyoxyalkylene block copolymers have beneficial utility as foam stabilizers in the production of open-cell flexible polyether polyurethane foams having reduced flammability. However, none of the latter mentioned patents exemplify the use of low molecular weight organosiloxane compositions described in this invention as foam stabilizers in the manufacture of low density flexible polyester polyurethane foam.
It is desirable, therefore, and is a primary object of this invention, to provide a process for manufacturing low density flexible polyester polyurethane foam utilizing as a foam stabilizer selected organosiloxane compositions having wide processing latitude.
A further object is to provide low density flexible polyester polyurethane foams characterized by desirable physical properties including high cell counts.
Yet another object is to provide solutions, consisting of an organosiloxane composition foam stabilizer and certain other component(s) of suitable compatability, to facilitate the handling of foam stabilizers in conventional polyester polyurethane foam formulations.
Various other objects and advantages of this invention will become apparent to those skilled in the art from the accompanying description and disclosure.